Telephone system



Nov. 7, 1933. R, F. STEHLIK 1,934,384

TELEPHONE SYSTEM Filed July 2 1931 Patented Nov. 7, 1933 FFlQlE TELEPHQNE SYSTEM ,Rudolph Frank Stehlik, Chicago, lllL, assignor to Associated Telephone and Telegraph Company, Chicago, 111., a corporation of Dela- Ware Application July 23, 1931, Serial No; 552,706, and in Great Britain July 29, 1930 14 Claims.

The present invention relates to telephone systems and its chief object is to provide simplifled circuit arrangements whereby the cost of providing automat'c switching apparatus may be reduced without rendering it in any way less reliable.

According to one feature of the invention the various switches in a group of automatic switches are allotted for use in a predetermined order without the use of a special allotting switch, and this is effected by arranging that the switches are normally maintained in an off-normal position with the exception of the switch which is next to be taken into use. 7

Another feature of the invention relates to the use of a single intermittently operated device to generate both ringing current and also impulses for erlecting the operation of switch magnets.

According to a further feature of the invention a relay arranged to be controlled by impu ses transmitted by the calling partys dial switch after a busy signal has been received to extend a speaking connection to a busy line.

The circuit connections of a preferred method of carrying the invention into effect employing link circuits comprising rotary switches as finder switches and connector switches, are shown in the accompanying drawing and the operations involved will now be described. The rotary switches shown are provided with a bank of eleven contacts and the conn ctor switch is arranged so that one of these contacts serves as a home position, the maximum capacity of this arrangement consequently 10 lines and is suitable for use'as a small private automatic exchange. Two link circuits are provided one of which is shown in detail while the other is represented only by its relays T and Hgconsequently with his arrangement two simultaneous convernot are possible. it will be assumed that the subscriber at the bstation connected to conductors 11 and 12 cri, a call by lifting his handset. Relay LE thereupon operates partially over its lower windii in the f -lowing circuit: battery, winding of start relay ST, lower winding of relay LE, contact conductor l2, loop at the calling substation, conductor 11 contact 14 to earth. Relay LE operates contact 15 only thereby connects ery through its upper winding to the private 1 contact of the calling line. The start re- ST, which common to all the line relays, wrates in series with relay LE and connects ear h over contact 23 to the relay T of all the li circuits. At the same time the tart relay ST completes a circuit for relay PC over: earth, contacts 24 and 31, winding of relay PC to battery, relay PC operates intermittently and at contact transmits impulses over the homing plate associated with the wiper 110 of the connector switch to restore the connector switch to its norreal position, the circuit for the connector switch magnet may be tracedas follows: earth, cont cts 3i) and 44, homing plate and wiper 110, lower winding of relay I, winding of magnet CM to battery. When the connector switch reaches its normal position a circuit is completed for relay T over: earth, contacts 23, 25 and 22, windin of relay T, contact 13, home contact and wiper 110 or" the connector switch, lower winding of clay I, winding of driving magnet CM to battery. 1

Relay T upon operating opens a point in the circuit of relay T of the second link circuit at contact 28 to prevent two finders hunting at the same time and connects the impulsing earth from contact 39 of relay PC'over contacts 44 and 36 to the winding of the driving magnet FM of the finder switch. Magnet FM thereupon intermittently energizes and de-energi es and steps the 0 wipers of the finder switch until wiper 19 engages the test contact of the calling line. This test contact will be marked by the presence of battery connected through the upper winding of relay LE and a circuit is thereupon completed 5 for the lower winding of relay H over contact 21. Relay l-I operates, opens the circuit of the magnet FM at contact 44, and opens the circuit of relay T at contact 22. Relay H also extends the calling loop to relay A at contacts 41 and 47. Relay A operates over the calling loop and at contact 52 completes a locking circuit for relay H which may be traced follows: battery, winding of magnet Cl -Ji, upper winding of relay H, contacts 71, 52 and i2 to earth. After its slow period, relay T releases and at contact 27 short: circuits the lower winding of relay H thereby rendering relay H slow to release. The earth connection from contact 27 is extended over contact 3'7 and wiper 19 to eliect the complete oper- 10o ation of relay LE over its upper winding, whereupon relay LE disconnects the normal battery and earth connections from the calling line at contacts 16 and 14. The start relay ST thereupon releases.

Relay A upon operating completes a circuit for relay I as follows: battery, winding of connector magnet CM, lower winding of relay I, wiper 110 and home contact of the connector switch, upper windingoi relay 1, contacts 52 and 42 to earth. 11o

Relay I upon operating changes the holding circuit of relay H to the following circuit: battery, winding of magnet CM, upper winding of relay H, contacts and 42 to earth, and completes a circuit for the dial tone and busy tone relay Bi) over the following circuit: battery, resistance 95, winding of relay Bl), contacts 67 and 48 to earth. Relay BD operates and short-circuits its winding at contact 96 whereupon it releases, relay BD consequently operates intermittently and dial tone is fed to the calling subscriber over contact 68, condenser 59 and thence over upper speaking conductor to the calling substation.

The calling subscriber hearing the dial tone will dial the number of the wanted subscriber which will be one of the digits 1(). In response to the train of impulses transmitted by the calling subscriber, relay A de-energizes intermittently, and a stepping circuit is thereby completed for magnet CM as follows: earth, contacts '42, 53, 26 and 45, lower winding of relay I, Winding of connector switch magnet CM to battery. The magnet CM is energized intermittently and steps the wipers onto the line of the wanted subscriber. The high resistance upper winding of relay I is disconnected when the connector switch moves oil normal but since relay I is slow to release it remains operated in response to the impulses through its low resistance lower winding.

At the end of the impulse train, relay I releases and completes a circuit for the ringing and busy tone start relay SR which in turn completes a ci cuit over contact 86 for relay ED, a circuit over contact 87 for the interrupter relays and a circuit over contact 83 for relay PC. it will be assumed first that the called line is busy, in this case no operations will take place in the link circuit but in response to the operation of relay SR, busy tone current will be fed over contacts 49, 57, 99 and 70, condenser 69, and thence over the upper speaking conductor to the calling substation.

The manner in which interrupted busy tone current is generated will now be descri ed. Due to the connection of earth at contact 86, relay 13D 0 crates intermittently in the manner previously described and a pulsating current is thereby caused to fiow through its winding. A circuit is completed over contacts 87, 51 and 61 for relay T1. Relay Tl operates, at contact 54 completes a circuit for relay and at contact 63 completes a circuit for the relay T3 extending over contacts 59 and 50. Relays T2 and T3 thereupon operate and relay T3 completes a locking circuit for itself at contact 58, at contact 65 closes a point in the circuit of relay T4 and at contact 61 opens the initial energizing circuit of relay Tl. After its slow period relay T1 releases, opens the circuit of relay T2 at contact. 64 and prepares a circuit for T4 at contact 65. After its slow release period relay T2 releases and at contact 62 completes a circuit for relay T4. Relay T4 operates and at contact 50 opens the locking circuit of relay T3 which after its slow release period releases and at contact 60 opens the circuit for relay T4. After its slow release eriod relay T4 releases and at contact 51 again completes the original circuit of relay T1, whereupon the cycle of the inter rupter relays is again started. The cycle is made up as follows:

(1) The operation of relay Tl followed by the operation of relays T2 and T3, whereupon contact 57 is closed.

(2) The slow release of relays T1 and T2 in turn, whereupon contact 57 is opened.

(3) The operation of relay T4, whereupon contact 49 is closed.

(4) The slow release of relays T3 and T4 in turn, whereupon contact 49 is opened.

When contact 49 or contact 57 is closed busy tone is fed over contacts 99 and 70, condenser 69 and thence over the upper speaking conductor to the calling substation.

The calling subscriber hearing the busy tone will replace hishandset whereupon the calling loop broken and relay A releases. The circuit of relay H is thereupon opened at contact 52 and this relay releases and opens the circuit for relay SE at contact 48.

If, however, the wanted line is idle, wiper 109 will encounter battery through the upper winding of line relay of the called subscriber, and relay CON will operate over its upper winding in the following circuit: earth, contacts 48 and 66, upper winding of relay CON, test wiper 109, test contact of called line, upper winding or" called subscribers line relay to battery. Relay CON upon operating locks up over its lower winding in the following circuit: earth, contacts 42 and 101, lower winding of relay CON to battery. Relay SR operates in the following circuit: battery, upper winding of relay SR, contact 77, upper winding of relay CON, contacts 106 and 48 to earth and causes the interrupter relays T1, T2, T3 and T4 to operate in the manner previously described. At the same time a circuit is completed at contact 88 for relay PC whereupon relay PC operates intermittently and connects earth alternately to the outer terminals of the left-hand winding 34 of the ringing transformer and alternating current is thereby induced in the secondary winding 35. Once in every cycle of the interrupter relay TlT4 contact 55 is opened and contact 56 is closed, the upper winding of relay ET is thereby transferred periodically from battery fed through resistance 54 to battery fed through the secondary winding 35 in which alternating current is being induced. Ringing current is thereby fed through the upper winding of relay RT, contacts 84 and 102, wiper 108, over the called line, through the called subscribers condenser and bell, and thence back over the upper speaking conductor, wiper 107, contacts 98 and '78 to earth. At the same time a ring-back tone is fed back to the calling party over the following circuit: ringing current fed through the upper winding of relay RT, contacts 84, 100 and 70, condenser 69 and thence over the upper speaking conductor to the calling substation.

- It will be noted that contact 56 is closed once in every cycle of the interrupter relays and consequently the interval between each connection of ringing current is twice that of the interval between each connection of busy tone.

When the called subscriber replies, a direct current loop is placed across the called line and relay RT thereupon operates in the following circuit: battery, resistance 54, contact 55, upper winding of relay RT, contacts 84 and 102, wiper 108 and bank contact, called loop, bank contact and wiper 107, contacts 98 and 78 to earth. Helay RT locks up over its lower winding and contacts 85, 104 and 42 to earth, at contact 77 it disconnects relay SR to cause the tone circuit to restore to normal and at contacts 79 and 83 it completes the speaking circuit between the calling and called lines. Conversation can now take place, talking battery being supplied to the substations of both subscribers through the windings of relay A. a

Relay A is maintained operated as long as either subscriber maintains his handset'oif the cradle switch, but when both subscribers have hung up, relay A releases and followed by the release of relay H in the manner previously described, in addition contact 42 isopened upon the release of relay H to release relays RT and CON.- As already mentioned, relay RT upon operating opened the circuit of relay SE at contact 7'7 and the tone circuit restored to normal, relay PC consequently ceased impulsing so that the magnets of the finder and connector switches will not be operated when the connector is released and the finder and connector switches will remain in the position which they occupied during conversation. It will be understood, however, that impulsing earth from relay PC also extended to the second link circuit so that if the connector switch of that link circuit is idle, it will have been restored to normal and that link circuit would consequently be taken into use in response to the initiation of a further call. It will be seen, therefore, that calls are allotted to the different speaking circuits in turn without the necessity of providing a separate allotting switch, the arrangement being such that a switch or relay in the speaking circuit remains in an off-normal condition until it is the turn of the speaking circuit to be taken into use.

When a subscriber is to be provided with prioiity service, so that he can extend connection to lines even they test busy, the contact associated with his line in the bank engaged by wiper 20 of the finder switch is connected to earth over conductor 13. The operations which take place are the same as those already described and if the wanted line is busy the calling subscriber will receive busy tone in the usual manner. If, however, he desires to establish connection with the busy line he dials an additional digit e. g. 1, which is not repeated to the connector magnet CM since relay I is not operated but causes relay RT to operate partially over the following circuit: battery, lower winding of relay RT, contacts 163, ad, 25, 53 and 42 to earth; relay RT closes contact and thereupon operates completely over the following circuit: battery, lower windof relay RT, contacts 85, 105 and 71, wiper 20 of the finder switch to earth on conductor 13. Relay RT thereupon connects thecalling loop at contacts 81 and 82 through the speaking condensers 111 and 112 to the busy line so that the calling subscriber can attract the attention of the wanted subscriber.

What I claim as new and desire to secure by Letters Patent is:-

1. In a telephone system, a plurality of automatic switches for completing telephone connections, each switch remaining in the position last used, and means for automatically restoring the n xt switch to be used to its normal position dur-- ing the establishment or" each connection.

2. In a telephone system, a plurality of auto- ;n tic switches for comple'" 1g telephone connecg in the position last ti us, each switch remai used, and common control apparatus for restoring said switches to normal one at a time to render them available for use.

3. In. a telephone system, a plurality of link circuits for completing telephone connections, each link comprising two rotary switches, and means for rendering said link circuits available for use one at a time in predetermined order, said means including ofi -normal contacts of one switch in each link circuit.

. 4. In atelephone system, two'link circuits for completing telephoneconnections, a finder switch and a connector switch ineach link circuit, the switches of a link'remaining in the position last used when the link is released, and means for restoring the connector of an idle link to its normal position'while a connection is beingfestab- 'lished over the other link; I

6. In a telephone system, subscribers lines, a

link circuit comprising a finder switch and a connector switch for establishing connections between said lines, means for marking certain of said lines in the banks of said finder switch, and means controlled by a subscriber from a marked line for completing a connection to a busy called line. I

'7. In a telephone system, subscribers lines, a link comprising a finder switch and a connector switch, means for marking certain of said lines in the banks of said finder switch, means responsive to the initiation of a call over one of said lines for associating said link with the calling line, means responsive to the dialling of a digit by the calling subscriber for operating said connector to extend his line to the desired called line, and means responsive to the dialling of a further digit in case the called line is busy and provided the calling subscribers line is marked in the banks of said finder switch for completing a talking connection to the busy called line.

8. In a telephone system, subscribers lines some of which are entitled to priority service, a link circuit comprising a finder switch and a connector switch for establishing connections between said lines, a relay in said connector switch, a circuit for said relay prepared when said finder switch connects with a calling line entitled to priority service, means controlled by the subscriber on such a line for completing said circult in case the called line is busy, and means controlled by said relay for completing a talking connection to the busy called line.

9.-In a. telephone system, subscribers lines automatic switching apparatus responsive to a dialled digit from a calling line for establishing a connection to. a desired called line, and means responsive to a furtherdialled digit andeffective only if the calling line is entitled to priority service for completing a talking connection to a busy called line.

10. In a telephone system, a link circuit comprising a finder switch and a connector switch for establishing connections between subscribers lines, a relay in said link circuit operated when said finder switch connects with a calling line to connect dial tone thereto, and means for releasing said relay after the operation of said connector switch into engagement with a desired called line to connect ringing current to the called line.

11. In a telephone system in which connections are established between subscribers lines over a link circuit comprising a fhider switch and a connector switch, a relay, means for intermittently operating said relay, and means controlled by said relay for generating impulses to operate the findnector to restore the same to normal, and means effective when the connector is restored for causing said generator to transmit impulses to said finder to cause the same to connect with the calling line.

14. In a telephone system, a link circuit comprising a finder and a connector, means responsive to a call for restoring said connector to normal and for preparing a start circuit for the said finder, and means for completing said start circuit upon the connector reaching normal.

RUDOLPH F. STEI-ILIK. 

